This is a chemoprevention trial of finasteride to reduce the incidence of prostate cancer in healthy men. Finasteride causes a profound reduction in circulating and cellular dihydrotestosterone, a potentially important agent in the initiation and progression of prostate cancer. The study will test the difference in the biopsy-proven prevalence of carcinoma of the prostate between a group of participants treated with finasteride and a group treated with placebo for seven years.